output_thread: added command DRAIN

This command manually drains the hardware buffer.  This is useful when
the player thread want to make sure that everything has been played.

src/output_all.c

@@ -495,6 +495,15 @@ audio_output_all_pause(void)
 	audio_output_wait_all();
 }
 
+void
+audio_output_all_drain(void)
+{
+	for (unsigned i = 0; i < num_audio_outputs; ++i)
+		audio_output_drain_async(&audio_outputs[i]);
+
+	audio_output_wait_all();
+}
+
 void
 audio_output_all_cancel(void)
 {

src/output_all.h

@@ -129,6 +129,12 @@ audio_output_all_wait(unsigned threshold);
 void
 audio_output_all_pause(void);
 
+/**
+ * Drain all audio outputs.
+ */
+void
+audio_output_all_drain(void);
+
 /**
  * Try to cancel data which may still be in the device's buffers.
  */

src/output_control.c

@@ -229,6 +229,15 @@ void audio_output_pause(struct audio_output *ao)
 	g_mutex_unlock(ao->mutex);
 }
 
+void
+audio_output_drain_async(struct audio_output *ao)
+{
+	g_mutex_lock(ao->mutex);
+	if (audio_output_is_open(ao))
+		ao_command_async(ao, AO_COMMAND_DRAIN);
+	g_mutex_unlock(ao->mutex);
+}
+
 void audio_output_cancel(struct audio_output *ao)
 {
 	g_mutex_lock(ao->mutex);

src/output_control.h

@@ -67,6 +67,9 @@ audio_output_play(struct audio_output *ao);
 
 void audio_output_pause(struct audio_output *ao);
 
+void
+audio_output_drain_async(struct audio_output *ao);
+
 void audio_output_cancel(struct audio_output *ao);
 void audio_output_close(struct audio_output *ao);
 void audio_output_finish(struct audio_output *ao);

src/output_internal.h

@@ -40,6 +40,13 @@ enum audio_output_command {
 
 	AO_COMMAND_CLOSE,
 	AO_COMMAND_PAUSE,
+
+	/**
+	 * Drains the internal (hardware) buffers of the device.  This
+	 * operation may take a while to complete.
+	 */
+	AO_COMMAND_DRAIN,
+
 	AO_COMMAND_CANCEL,
 	AO_COMMAND_KILL
 };

src/output_thread.c

@@ -450,6 +450,19 @@ static gpointer audio_output_task(gpointer arg)
 			   the new command first */
 			continue;
 
+		case AO_COMMAND_DRAIN:
+			if (ao->open) {
+				assert(ao->chunk == NULL);
+				assert(music_pipe_peek(ao->pipe) == NULL);
+
+				g_mutex_unlock(ao->mutex);
+				ao_plugin_drain(ao->plugin, ao->data);
+				g_mutex_lock(ao->mutex);
+			}
+
+			ao_command_finished(ao);
+			continue;
+
 		case AO_COMMAND_CANCEL:
 			ao->chunk = NULL;
 			if (ao->open)